1. Field of the Disclosure
This disclosure relates to a liquid crystal display device, and more particularly to a liquid crystal display device adapted to control a viewing angle.
2. Description of the Related Art
As the information society grows, flat display devices capable of displaying information have become widely developed. These flat display devices include liquid crystal display (LCD) devices, organic electro-luminescence display (OLED) devices, plasma display devices, and field emission display devices.
Among the above display devices, LCD devices have the advantage in that they are light, small, and can provide a low power drive and a full color scheme. Accordingly, LCD devices have become widely used for mobile phones, navigation systems, portable computers, televisions and so on. The LCD device controls the transmittance of a liquid crystal on a liquid crystal panel, thereby displaying a desired image.
The LCD devices include a TN (Twisted Nematic) mode LCD device and an IPS (In Plane Switching) mode LCD device. The TN mode LCD device displays an image using a vertical electric field, while the IPS mode LCD device displays an image using a horizontal electric field.
More specifically, the TN mode LCD device enables a liquid crystal to be driven by a vertical electric field between pixel electrodes arranged on a lower substrate and a common electrode disposed on an upper substrate, in order to display images. However, there is a disadvantage in that the TN mode LCD device is limited to a relatively narrow viewing angle.
On the other hand, the IPS mode LCD device forces a liquid crystal to be driven by a horizontal electric field between pixel electrodes and common electrodes arranged parallel to each other on a lower substrate, thereby displaying images. The IPS mode LCD device provides a relatively wide viewing angle in comparison with that of the TN mode LCD device. In other words, the IPS mode LCD device has the advantage of a wider viewing angle. As such, the IPS mode LCD device is widely used.
Images displayed on the LCD device are generally viewable to other persons. However, for recently reinforced information security, it is keenly necessary for screens not to be viewable to other adjacent persons.
In order to meet this requirement, an LCD device adapted to control a viewing angle whether wide or narrow is proposed. The LCD device can prevent a displayed image from being viewed by adjacent persons whose eyes are positioned on the same line as those of a user. However, there is a disadvantage in that the image displayed on the LCD device is viewed by adjacent persons whose eyes are at higher positions than those of a user. In other words, the image on the LCD device is visible to persons adjacent to the user from upwardly diagonal directions.